This invention relates to a transmission assembly for a working vehicle comprising a front housing and a transmission case which are arranged in series in a longitudinal direction of the vehicle and are fastened together. The front housing includes at its front end portion an engine flywheel and the transmission case includes at least one speed change mechanism. More particularly, the present invention relates to a transmission assembly in which two fluid-operated supplementary speed change mechanisms are provided within the front housing in such a manner that does not lengthen the front housing.
In a fluid-operated speed change mechanism having plural fluid-operated clutches, fluid passages communicated to the plural clutches are formed in a transmission shaft on which the plural clutches are mounted. The fluid passages in the transmission shaft will rotate together with the rotation of the transmission shaft. Thus, rotary joints are required for connecting the fluid passages in the transmission shaft to stationary fluid passages. In a transmission assembly in which two fluid-operated speed change mechanisms are provided, such rotary joints are formed in outer circumferences of two transmission shafts, on which respective plural fluid-operated clutches of the respective change mechanisms are mounted, such that two sets of the rotary joints are placed within two separate bearing support members which support the two transmission shafts, as shown, for example, in U.S. Pat. No. 6,044,720. Each of the bearing support members is made thick in a longitudinal direction of the vehicle because of the plural rotary joints included therein. Thus, the two separate bearing support members each of which is thick will lengthen the transmission assembly and, therefore, the vehicle.
Accordingly, a primary object of the present invention is to provide a novel transmission assembly for a working vehicle in which two supplementary speed change mechanisms are provided in a front housing, having an engine flywheel at a front end portion thereof, with preventing the front housing from being lengthened by taking measures how to form the rotary joints between rotatable and stationary fluid passages.
An attendant object of the invention is to provide a novel transmission assembly which is as simple in structure as possible.
Another attendant object is to provide a novel transmission assembly which is easy in assembling.
The present invention relates to a transmission assembly in a working vehicle comprising a front housing (1) and a transmission case (2) which are arranged in series in a longitudinal direction of the vehicle and are fastened together. The front housing includes at its front end portion an engine flywheel (6), and the transmission case includes at least one speed change mechanism (14, 15). The transmission assembly according to the present invention is characterized in:
that there are provided within the front housing (1) two fluid-operated supplementary speed change mechanisms (9, 10) which are disposed before and behind a bearing support wall (4) and are connected to each other in series, the bearing support wall dividing the inside of the front housing into front and rear chambers, one of the supplementary speed change mechanisms being formed into a direction-reversing mechanism and the other of the supplementary speed change mechanisms being formed into a high/low speed-selecting mechanism, and
that two transmission shafts (8, 12), on which fluid-operated clutches (38F, 38R, 45, 46) of the supplementary speed change mechanisms (9, 10) are mounted, are disposed non-coaxially with each other and are supported by the bearing support wall (4), rotary joints (54F, 54R, 54L, 55H, 55L) for connecting fluid passages (51F, 51R, 51L, 52H, 52L), which are formed in the two transmission shafts and are communicated with the fluid-operated clutches, to stationary fluid passages being formed in outer circumferences of the two transmission shafts (8, 12) at an inside of the bearing support wall (4).
In the transmission assembly in which two supplementary speed change mechanisms are provided within the front housing before and behind a bearing support wall which divides the inside of the front housing into front and rear chambers, the two transmission shafts on which fluid-operated clutches are mounted are disposed, according to the present invention, non-coaxially with each other and the rotary joints (54F, 54R, 54L, 55H, 55L) for connecting fluid passages in the two transmission shafts are particularly formed in the outer circumferences of the two transmission shafts (8, 12) at an inside of the single bearing support wail (4). Thus, only the single support wall (4) is used for forming the rotary joints, so that the front housing and, therefore, the vehicle are prevented from being lengthened.
For simplifying the structure of the transmission assembly, it is preferred that one of the two fluid-operated clutches (45) of the high/low speed-selecting mechanism (10) is formed into a fluid-actuated clutch which is actuated by the action of fluid pressure and is disactuated by the action of a spring (45a) whereas the other of the two fluid-operated clutches (46) of the high/low speed-selecting mechanism is formed into a spring-actuated clutch which is actuated by the action of a spring (46a) and is disactuated by the action of fluid pressure, the two fluid-operated clutches (45, 46) being adapted to be supplied with fluid pressure at a same time through a single fluid passage (52H) formed in the transmission shaft (12) on which the two fluid-operated clutches are mounted. According to this structure, an operating fluid passage to be formed in the above-referenced transmission shaft can be made single.
For an easy assembly, it is preferred that the bearing support wall (4) is detachably secured to the front housing (1).
For an easy assembly, too, it is preferred that there is detachably secured to an outer wall of the front housing (1) a fluid passage-forming plate (57) including fluid passages (61F, 61R, 61L, 62H, 621) which are in fluid communication with the rotary joints (54F, 54R, 54L, 55H, 55L), the fluid passages and the rotary joints being connected through pipes (63F, 63R, 63L, 64H, 64L) which extend through openings (65, 66) formed in the outer wall of the front housing (1).
For simplifying the structure of the transmission assembly set forth above, it is preferred that a directional control valve (90) for the direction-reversing mechanism (9) and a directional control valve (76) for the high/low speed-selecting mechanism (10) are attached to the fluid-passage-forming plate (57). The directional control valves (90, 76) are provided at locations as near to the supplementary speed change mechanisms (9, 10) as possible, so that lowering of fluid pressure between the directional control valves and the two supplementary speed change mechanisms is small.
It is often the cases that the fluid-operated clutches of the direction-reversing mechanism are selectively engaged in a slipping condition by selectively reducing fluid pressure applied thereto so as to achieve running of the vehicle at a reduced speed. According to a preferred embodiment of the present invention, the transmission shaft (8) of the direction-reversing mechanism (9), which is disposed at an upstream side of the high/low speed-selecting mechanism (10), is arranged at a level higher than the level of the transmission shaft (12) of the high/low speed-selecting mechanism. According to this structure, the transmission shaft (8), on which the fluid-operated clutches (38F, 38R) of the direction-reversing mechanism are mounted, can be arranged at such a high level that the fluid-operated clutches are not immersed in lubricant oil which is accomodated in a low level within the front housing. Thus, the control for reducing fluid pressure applied to the fluid-operated clutches is not damaged by lubricant oil which might otherwise exist between frictional elements of the fluid-operated clutches, so that the fluid pressure-reducing control can be performed reliably.
According to another preferred embodiment of the present invention, the bearing support wall (4) is detachably secured to the front housing (1) and another bearing support wall (5) is detachably secured to the front housing at a location spaced from and behind the bearing support wall, one of the supplementary speed change mechanisms (9) being disposed before the bearing support wall (4) whereas the other of the supplementary speed change mechanisms (10) being disposed between the bearing support wall (4) and the another bearing support wall (5). According to this structure, the fluid-operated direction-reversing mechanism and high/low speed-selecting mechanism both requiring a high accuracy can be assembled into the front housing as a package for which the bearing support wall and another bearing support wall are used as support members for the supplementary speed change mechanisms.